Process for the enrichment or separation of organic substance mixtures

The present invention relates to a process for the enrichment or separation of salts of organic carboxylic acids from non-salt organic compounds, in which a solution of those salts and compounds in a low molecular weight alkanol is brought into contact with one side of a semipermeable membrane consisting of a perfluorosulfonic acid polymer, the pure low molecular weight alkanol being present on the opposite side of the membrane.

U.S. Pat. No. 4,846,977 describes a separating process for mixtures of polar and non-polar liquids using semipermeable membranes consisting of perfluorosulfonic acid polymers. Suitable polar liquids are, for example, lower alkanols and especially water, and suitable non-polar liquids are, for example, hydrocarbons, ethers, ketones, esters or organic acids.

It has surprisingly been found that using the same membranes it is also possible to enrich or separate mixtures of salts of organic carboxylic acids and non-salt organic compounds in the form of solutions in low molecular weight alkanols.

The invention relates to a process for the enrichment or separation of salts of organic carboxylic acids from non-salt organic compounds using a semipermeable membrane consisting of a perfluorosulfonic acid polymer or a salt of such a polymer, wherein a solution of the salts and organic compounds in an unsubstituted or C 1 -C 3 alkoxy-substituted C 1 -C 4 alkanol, mixtures of said alkanols or mixtures of said alkanols with ethers is brought into contact with one side of the membrane and the pure solvent is present on the opposite side of the membrane.

The concentration of the salts and organic compounds is preferably from 0.0001 to 10%, especially from 0.001 to 5% and more especially from 0.001 to 3% by weight, based on the solution.

The thickness of the membrane can be, for example, from 5 to 300 μm, preferably from 20 to 200 μm.

Perfluorosulfonic acid polymers and salts of those polymers are known and are described, for example, in U.S. Pat. No. 4,846,977. Some of those polymers are commercially available under the brand name NAFION® (DuPont).

In a preferred embodiment, the membrane consists of a perfluorosulfonic acid polymer having recurring structural elements of formula I ##STR1## wherein R 1 and R 2 are each independently of the other F or C 1 -C 10 perfluoroalkyl, w is a number from 5 to 15, x is a number from 0 to 6, y is a number from 1 to 16, z is a number from 0 to 16, and M is H.sup.⊕, an ammonium cation or a metal cation, R 1 and R 2 are preferably fluorine or C 1 -C 3 perfluoroalkyl, especially fluorine or trifluoromethyl and more especially fluorine. In formula I, preferably w is a number from 5 to 10, x is a number from 0 to 2, y is a number from 1 to 6 and z is a number from 0 to 6, especially from 0 to 2.

M as an ammonium cation may be NH 4 .sup.⊕ or an ammonium cation of a primary, secondary or tertiary open-chain amine having preferably from 1 to 20, especially from 1 to 12, carbon atoms, or an ammonium cation of a monocyclic or bicyclic secondary or tertiary amine or of a tricyclic tertiary amine having preferably from 4 to 12 carbon atoms.

M as a metal cation may be a mono- to tri-valent cation of a metal of the main and subsidiary groups, the transition metals and the noble metals. Mono- or di-valent metal cations are preferred. Examples of metals are Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, In, Sn, Pb, Cu, Ag, Au, Zn, Cd, Hg, Cr, Mo, Mn, Fe, Co, Ni, Rn, Rh, Pd, Ir, Pt, Sb, Bi, and also the group of the rare earth metals. Preferred metals are the alkali metals and alkaline earth metals, Cu, Ag, Au, Fe, Co, Ni, Zn, Cd and Mn.

In a preferred embodiment, M is NH 4 .sup.⊕, an ammonium cation having a total of from 1 to 18 carbon atoms, or a mono- to tri-valent metal cation. M is more especially an alkali metal cation or Ag.sup.⊕.

The permeation of a salt of an organic carboxylic acid or of a non-salt organic compound can be influenced by the cation M chose. When membranes having relatively small monovalent cations are used, it is generally the non-salt compound that permeates preferentially. When relatively large mono- or poly-valent cations are used, it is generally the salt that permeates preferentially.

It has been found that in especially favourable cases the salt is retained virtually completely when M in formula I is Ag.sup.⊕. Conversely, the relatively non-polar organic compound is retained virtually completely when M in formula I is Cs.sup.⊕. Preference is therefore given to a process wherein M in formula I is Ag.sup.⊕ or Cs.sup.⊕.

The alkanol used as solvent contains from 1 to 4 carbon atoms and preferably from 1 to 3 carbon atoms. It may be substituted, for example by methoxy or ethoxy. Examples thereof are methanol, ethanol, n- and iso-propanol, n-, iso- and tert-butanol, methoxyethanol, ethoxyethanol, propoxyethanol, 1-methoxypropan-3-ol and 2-methoxypropan-1-ol. Preferred solvents are methanol, ethanol, 1- or 2-propanol and 2-methoxyethanol. It is also possible to use mixtures of alkanols with one another or with ethers, for example diethyl ether or ethylene glycol dimethyl ether.

The salt of the organic carboxylic acid may be an ammonium or metal salt, for example NH 4 .sup.⊕, an ammonium cation of a primary, secondary or tertiary amine having a total of from 1 to 20 carbon atoms, an alkali metal salt or alkaline earth metal salt. Alkali metal salts and ammonium salts are preferred. NH 4 .sup.⊕ and Li.sup.⊕ salts are especially preferred.

The organic carboxylic acid may be, for example, a mono-, di-, tri- or tetra-carboxylic acid. Aliphatic, cycloaliphatic, aromatic and heterocyclic or heteroaromatic monocarboxylic acids containing from 1 to 18 carbon atoms, preferably from 1 to 12 carbon atoms, are preferred.

In a preferred embodiment, the organic acid corresponds to formula (II)

R.sub.3 --X--COOH (II)

wherein X is a direct bond, C 1 -C 4 alkylene, C 2 -C 4 alkylidene or C 2 -C 4 alkenylene, R 3 is H or C 1 -C 12 alkyl, C 2 -C 12 alkenyl, C 2 -C 12 alkynyl, C 3 -C 12 cycloalkyl, C 3 -C 12 cycloalkenyl, C 6 -C 16 aryl, C 3 -C 12 heterocycloalkyl, C 3 -C 12 heterocycloalkenyl, C 6 -C 16 heteroaryl, each of which is unsubstituted or substituted by --OH, --SH, --CN, --NO 2 , halogen, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, C 1 -C 6 alkylthio or by C 1 -C 6 alkyl-Y-- in which Y is --CO--, --SO--, --SO 2 --, --CO--O--, --O--CO--, --CO--NR 4 R 5 -- or --NR 4 R 5 --CO--, and R 4 and R 5 are each independently of the other H, C 1 -C 6 alkyl, C 2 -C 4 hydroxyalkyl or R 4 and R 5 together are tetramethylene, pentamethylene or 3-oxapentyl-1,4-ene.

Examples of R 3 as alkyl, which may be linear or branched, are methyl, ethyl, n- and iso-propyl, n- and iso-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl.

Examples of R 3 as alkenyl, which may be linear or branched, are vinyl, crotonyl, allyl, but-1-en-1-yl, but-1-en-2-yl, but-1-en-3-yl, but-1-en-4-yl, but-2-en-1-yl, but-2-en-2-yl, but-2-en-4-yl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl and dodecenyl.

Examples of R 3 as alkynyl, which may be linear or branched, are ethynyl, prop-2-yn-1-yl, prop-2-yn-3-yl, butynyl, pentynyl, hexynyl, heptynyl, octynyl, decynyl and dodecynyl.

R 3 as cycloalkyl and cycloalkenyl preferably contains from 4 to 8 carbon atoms, especially 5 or 6 carbon atoms. Examples thereof are cyclopropyl and cyclopropenyl, cyclobutyl and cyclobutenyl, cyclopentyl and cyclopentenyl, cyclohexyl and cyclohexenyl, cycloheptyl and cycloheptenyl, cyclooctyl and cyclooctenyl.

R 3 as aryl preferably contains from 6 to 12 carbon atoms. Some examples thereof are phenyl, biphenyl and naphthyl.

R 3 as heterocycloalkyl and heterocycloalkenyl preferably contains from 4 to 8, especially from 4 to 6, ring carbon atoms. Preferred hetero atoms are those from the group O, S and NR 6 wherein R 6 is H, C 1 -C 6 alkyl or C 1 -C 7 acyl. R 3 as heteroaryl preferably contains from 4 to 11 ring carbon atoms and preferably hetero atoms from the group O, S and --N═. Some examples of heterocycles are pyrrolidine, tetrahydrofuran, tetrahydrothiophene, pyrroline, dihydrofuran, dihydrothiophene, indane, dihydrocoumarone, dihydrobenzothiophene, carbazole, dibenzofuran, dibenzothiophene, pyrazolidine, imidazolidine, pyrazoline, imidazoline, benzimidazolidine, oxazolidine, oxazoline, thiazolidine, thiazoline, isooxazolidine, isooxazoline, isothiazolidine, isothiazoline, benzoxazolidine, benzisooxazolidine, benzthiazolidine, 1,2,3- or 1,2,4-triazolidine, 1,2,3- or 1,2,4-triazoline, 1,2,3- or 1,2,4-oxazolidine or -oxazoline, piperidine, di- and tetra-hydropyridine, dihydro- and tetrahydro-pyran, di- and tetra-hydrothiopyran, piperazine, dehydropiperazine, morpholine, thiomorpholine, 1,3- and 1,4-dioxane, 1,4-dithiane, azepan, 1,3-dioxolane, 1,3-dithiolane, pyrrole, indole, imidazole, benzimidazole, furan, thiophene, benzofuran, benzothiophene, carbazole, dibenzofuran, dibenzothiophene, oxazole, isooxazole, thiazole, isothiazole, benzoxazole, benzothiazole, pyridine, pyrimidine, pyrazine, pyridazine, quinoline, isoquinoline, acridine, chromene, chromane, pyran, thiapyran, phenazine, phenoxazine, phenolthiazine and purine.

Examples of X in formula II are methylene, ethylene, 1,2- or 1,3-propylene, 1,2-, 1,3- or 1,4-butylene, ethylidene, 1,1- or 2,2-propylidene, 1,1- or 2,2-butylidene, ethenylene, prop-1-en-1,3- or -1,2- or -2,3-ylene.

In a preferred embodiment, the salt is a Li.sup.⊕ or NH 4 .sup.⊕ salt of a carboxylic acid from the group furan-2-carboxylic acid, benzoic acid, methylbenzoic acid, phenylacetic acid, cinnamic acid, sorbic acid or a C 2 -C 8 alkanecarboxylic acid.

The non-salt organic compound preferably contains from 2 to 20, especially from 2 to 16 and more especially from 2 to 12, carbon atoms. The organic compound is especially an ester of an organic monocarboxylic acid having a total of from 2 to 16 carbon atoms, an ether having from 2 to 12 carbon atoms, a ketone having from 3 to 16 carbon atoms or an alcohol having from 5 to 16 carbon atoms.

In a preferred embodiment, the organic compound is a C 1 -C 6 alkyl ester of furan-2-carboxylic acid, benzoic acid, methylbenzoic acid, phenylacetic acid, cinnamic acid, sorbic acid or an C 2 -C 8 alkanecarboxylic acid; a C 5 -C 12 alkanol or benzyl alcohol; a dialiphatic ketone having from 3 to 10 carbon atoms, a C 1 -C 6 alkyl phenyl ketone, or diphenyl ketone; or a dialiphatic ether having from 2 to 8 carbon atoms, C 1 -C 6 alkyl phenyl ether, or diphenyl ether.

The membrane can be constructed in various forms for carrying out the process according to the invention and can be incorporated into separating modules of customary design. For example, flat membranes or asymmetric membranes can be combined to form two-chamber or multi-chamber systems. It is also possible to use tubular membranes or hollow fibres which are generally used in the form of bundles. In order to increase mechanical stability the membranes can be mounted on a supporting framework.

The process according to the invention is generally carried out at room temperature. In order to obtain a sufficient rate of flow it is advantageous to establish increased pressure on the solution side. The pressure is preferably from 1 to 10 MPa, more especially from 1 to 6 MPa. In a special embodiment, the process is carried out in accordance with the counter-current principle.

The process according to the invention can be used, for example, as an enrichment or purification process or for recovering or separating reactants or secondary products from reaction residues or reaction mixtures or for the isolation or purification of intermediates, especially when thermally unstable substances are involved.

The following Examples illustrate the invention in more detail.

EXAMPLES 1-37

a) Manufacture of the membranes

The starting material used is a commercially available polymeric perfluorosulfonic acid membrane (H form) (Nafion®-117, DuPont) that is approximately 200 μm thick. For the purpose of conversion into the salt form, the membrane is placed for 1 to 30 days in a 1:1 mixture consisting of methanol and a 1M aqueous solution of the hydroxide or chloride of the desired cation. The membrane is then washed with distilled water and methanol. Before use, the membrane is placed in the respective solvent until equilibrium swelling has taken place (1 to 5 days). For the manufacture of membranes having silver cations, sodium salts of the perfluorosulfonic acid membrane are used as starting material and are reacted with silver nitrate.

b) Permeation tests

In the centre of a pressure cell, the membrane (diameter 4.7 cm) is mounted in the holder. Each chamber is connected to a reservoir for the solution or the pure solvent to which a pump is connected. The reservoirs are mounted on scales. Between the reservoirs and the pumps there are arranged conductivity cells and between the outlet and the reservoirs there are arranged UV detectors. A pressure of 2.5 MPa is established on the solvent side and the solution and the solvent are circulated in the same direction. 14 C measurements are taken using a liquid scintillation detector. The measurement data are evaluated using a computer program. The detectors are each calibrated with the organic compound and the salt of the carboxylic acid and the calibration curves are converted into algorithms from which the desired data are calculated.

The selectivity S is defined as follows, G P being the proportion by weight in the permeate and G L being the proportion by weight in the solution: ##EQU1##

Further data can be found in Tables 1 and 2 below.

__________________________________________________________________________

Metal

cation

in the Carboxylic

Relatively non-polar

No. membrane Solvent acid salt organic compound

__________________________________________________________________________

1 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

2 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

3 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

4 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

5 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

6 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

7 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

8 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

9 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

10 Li.sup.⊕

methanol Li cinnamate

furan-2-carboxylic

acid ethyl ester

11 Li.sup.⊕

methanol Li cinnamate

benzyl alcohol

12 Li.sup.⊕

methanol p-toluic acid Li salt

p-toluic acid ethyl ester

13 Li.sup.⊕

methanol phenylacetic acid

phenylacetic acid methyl

Li salt ester

14 Li.sup.⊕

methanol benzoic acid Li salt

benzoic acid methyl ester

15 Li.sup.⊕

methanol sorbic acid Li salt

sorbic acid ethyl ester

16 Li.sup.⊕

methanol Li cinnamate

acetophenone

17 Li.sup.⊕

methanol Li cinnamate

methyl phenyl ether

18 Li.sup.⊕

methanol Li acetate

methyl acetate

19 Li.sup.⊕

2-methoxyethanol

Li cinnamate

methyl cinnamate

20 Na.sup.⊕

methanol Li cinnamate

methyl cinnamate

21 Na.sup.⊕

ethanol Li cinnamate

methyl cinnamate

22 K.sup.⊕

methanol Li cinnamate

methyl cinnamate

23 K.sup.⊕

methanol Li cinnamate

methyl acetate

24 Ag.sup.⊕

methanol Li cinnamate

methyl cinnamate

25 Ag.sup.⊕

methanol Li cinnamate

methyl cinnamate

26 Cs.sup.⊕

methanol Li cinnamate

methyl cinnamate

27 Cs.sup.⊕

methanol Li cinnamate

methyl cinnamate

28 Ni.sup.2⊕

methanol Li cinnamate

methyl cinnamate

29 Co.sup.2⊕

methanol Li cinnamate

methyl cinnamate

30 Cu.sup.2⊕

methanol Li cinnamate

methyl cinnamate

31 NH.sub.4.sup.⊕

methanol Li cinnamate

methyl cinnamate

32 N(C.sub.4 H.sub.9).sub.4.sup.⊕

methanol Li cinnamate

methyl cinnamate

33 quinuclidinium

methanol Li cinnamate

methyl cinnamate

(1-azabicyclo

[2.2.2]octane)

34 Li.sup.⊕

methanol/di-

ammonium benzoate

methyl acetate

ethylene glycol

dimethyl ether 1:1

35 Li.sup.⊕

methanol Li benzoate

acetophenone

36 Li.sup.⊕

methanol ammonium benzoate

methyl benzoate

37 Li.sup.⊕

methanol Li cinnamate

methyl cinnamate

38 Li.sup.⊕

methanol octylammonium

methyl cinnamate

cinnamate

39 octylammonium.sup.⊕

methanol Li cinnamate

methyl cinnamate

40 Li.sup.⊕

methanol di-Li phthalate.sup.1

methyl benzoate

41 Li.sup.⊕

methanol di-Li phthalate.sup.1

tris(2-ethylhexyl)trimellitate

42 Li.sup.⊕

methanol tri-Li trimellitate.sup.2

dimethyl phthalate

43 Li.sup.⊕

methanol tetra-Li methyl benzoate

pyromellitate.sup.3

44 Li.sup.⊕

methanol di-Li 2-carboxy-

methyl cinnamate

cinnamate.sup.4

__________________________________________________________________________

.sup.1 98% dilithium salt + 2% monolithium salt

.sup.2 35% trilithium salt + 65% dilithium salt

.sup.3 45% tetralithium salt + 55% trilithium salt

.sup.4 65% dilithium salt + 35% monolithium salt

__________________________________________________________________________

Permea- Relatively non-

Amounts of

tion rate Carboxylic acid salt

polar organic comp.

components in

(mg ·

Detection

(amount start of test)

(amount start of test)

Test

permeate (mg)

min.sup.-1 ·

[UV (nm)/

Amount

Conc. Amount

Conc. time Organic

Selec-

No. cm.sup.-2)

C 14] (mg) (wt. %)

(mg) (wt. %)

(min.)

Salt

compound

tivity

__________________________________________________________________________

1 1.675

305 48.75

0.00975

1.25 0.00025

1080

0.714

0.340 18.7

2 1.583

305 45.00

0.00900

5.00 0.00100

1080

0.280

0.342 11.0

3 1.737

305 35.00

0.00700

15.00

0.00300

1050

0.425

1.005 5.5

4 1.721

305 25.00

0.00500

25.00

0.00500

1080

0.399

1.321 3.3

5 1.725

305 15.00

0.00300

35.00

0.00700

1080

0.300

1.864 2.7

6 1.741

305 5.00 0.00100

45.00

0.00900

1080

0.159

2.484 1.7

7 1.749

305 1.25 0.00025

48.75

0.00975

1050

0.044

2.828 1.6

8 1.767

305 5.00 0.00100

5.00 0.00100

1080

0.085

0.276 3.3

9 1.732

305 250.00

0.05000

250.00

0.05000

1080

4.176

12.974

3.1

10 1.232

260 250.00

0.05000

250.00

0.05000

1080

2.379

14.467

6.1

11 1.207

260 250.00

0.05000

250.00

0.05000

1080

2.173

34.200

15.7

12 1.685

255 25.00

0.00500

25.00

0.00500

1080

0.495

1.473 3.0

13 1.653

250 250.00

0.05000

250.00

0.05000

1080

4.617

18.687

4.1

14 1.690

255 250.00

0.05000

250.00

0.05000

1080

4.465

19.138

4.3

15 1.680

275 75.00

0.00500

75.00

0.00500

1050

0.787

1.506 1.9

16 0.717

280 250.00

0.05000

250.00

0.05000

1080

2.165

17.186

7.9

17 1.083

280 250.00

0.00500

250.00

0.05000

1040

2.187

14.878

6.8

18 1.284

C 14 7.50 0.00500

7.50 0.00500

1320

0.260

1.980 10.0

19 0.350

310 125.00

0.02500

125.00

0.02500

270

0.194

0.381 2.0

20 0.563

305 25.30

0.00500

25.30

0.00500

1080

0.170

0.569 3.4

21 0.067

300 25.00

0.00500

25.00

0.00500

1080

0.010

0.171 18.0

22 0.024

305 25.30

0.00500

25.30

0.00500

3240

0.295

0.443 1.5

23 0.010

C 14 10.00

0.00500

10.00

0.00500

5730

0.049

0.302 6.5

24 0.358

305 25.30

0.00500

25.30

0.00500

6500

0.000

7.400 ∞

25 0.189

305 1500.00

1.00000

3000.00

2.00000

1080

0.146

37.044

253.7

26 0.020

305 25.30

0.00500

25.30

0.00500

3600

0.390

0.000 0.0

27 0.037

305 1500.00

1.00000

1500.00

1.00000

260

0.234

0.000 0.0

340

0.260

0.077 0.3

28 0.031

305 25.30

0.00500

25.30

0.00500

2400

0.327

0.071 0.2

29 0.033

305 25.30

0.00500

25.30

0.00500

3510

0.772

0.466 0.6

30 0.064

305 25.30

0.00500

25.30

0.00500

2700

0.042

1.842 0.3

31 0.604

305 25.30

0.00500

25.00

0.00500

1080

0.331

0.719 2.2

32 0.314

305 25.30

0.00500

25.00

0.00500

1080

0.032

0.512 16.1

33 0.090

305 25.30

0.00500

25.00

0.00500

1080

0.040

0.116 2.9

34 0.352

C 14 10.00

0.00500

10.00

0.00500

4350

1.880

3.780 2.6

35 0.945

255 250.00

0.05000

250.00

0.05000

1350

1.586

15.854

10.0

36 1.740

255 250.00

0.05000

250.00

0.05000

1680

8.839

29.195

3.3

37 1.422

305 5000.00

1.0000

5000.00

1.00000

60 4.800

7.672 1.6

38 1.483

305 25.00

0.00500

25.00

0.00500

2070

1.024

3.093 3.3

39 1.099

305 25.00

0.00500

25.00

0.00500

2040

0.441

2.602 6.5

40 1.400

270 75.00

0.01500

75.00

0.01500

2040

1.216

14.340

14.3

41 1.392

270 75.00

0.01500

75.00

0.01500

2040

1.547

10.779

8.0

42 1.464

270 75.00

0.01500

75.00

0.01500

2040

1.601

13.096

9.7

43 1.587

270 2.50 0.00050

2.50 0.00050

2520

0.001

0.105 109.6

44 1.563

305 75.00

0.01500

75.00

0.01500

2040

1.434

9.361 7.3

__________________________________________________________________________